The automotive industry has had notable success in the reduction of regulated gaseous emissions from the use of hydrocarbon fuels in mass produced automobiles. For gasoline spark ignited engines, the gaseous emissions fall into two categories:
(1) evaporative emissions--which relate to unburned fuel vapors escaping from the vehicle's fuel tank, and PA1 (2) tailpipe emissions--which relate to emissions from the exhaust of the engine and include unburned and partially burned fuel, carbon monoxide, and oxides of nitrogen. PA1 obtaining a data value representative of the concentration of purge fuel vapors in the purge gas, PA1 operating a purge valve to permit the purge gas to be drawn into the cylinder of the internal combustion engine, PA1 determining an additional amount of fuel to be injected into the cylinder using the data value, PA1 injecting the additional fuel into the cylinder, and PA1 adjusting the data value if the total amount of fuel provided to the cylinder is greater than or less than a desired amount of fuel.
In the mid 1970s, catalytic converters and closed loop fuel control was adopted almost universally in the United States and progressively in other countries. As stricter emission control requirements were written into law, microprocessor-controlled fuel injection eventually became widespread, allowing for more elaborate and sophisticated control systems and fuel control strategies.
Early automotive control systems often used emulations of the mechanical controls that had been replaced by electronically-actuated devices. Simple physical and empirical strategies with primarily tabular calibrations were used in order to be compatible with the limited microprocessor capacity on-board the vehicle. Current state-of-the-art low emission systems utilize more advanced controls strategies that include mathematics and physics-based models of the complex chemical, thermodynamic, mechanical, and electrical processes that exist in the automobile. This modeling and control strategy is implemented using software which provides designers with a mix of advanced controls techniques and thrifty empiricism that they can use in providing efficient and effective engine control logic.
In state-of-the-art low emission gasoline vehicles, both evaporative emissions and tailpipe emissions have been reduced by more than 90% from previous uncontrolled levels. The reduction in evaporative emissions has been achieved largely by use of evaporative emission control systems that utilize a charcoal canister to store fuel vapors from the fuel tank, with periodic purging of the vapors into the air intake manifold of the engine where they are drawn into the engine cylinders and burned. However, the objective of further reducing the emissions to near zero levels gives rise to a conflict between the need for aggressive purging of the charcoal canister to control evaporative emissions and extremely precise control of engine Air/Fuel ratio for tailpipe emissions control. For example, the design of high pressure fuel injection systems has often included the use of high-flow re-circulation of fuel (pumped from the fuel tank to the engine and back to the tank). This would allow the fuel injectors to be maintained at lower operating temperatures, even in applications where underhood temperatures and fuel injector location would otherwise have resulted in excessive fuel injector temperatures. This has helped avoid phenomena such as vapor lock and is also considered desirable for the longevity and precision of the fuel injector. However, this fuel control approach is at odds with the need to keep tank temperatures low to avoid evaporative running losses in extreme conditions. In addition, new requirements for On-Board Refueling Vapor Recovery (ORVR), On-board Diagnostic (OBD II and EOBD) and real-time and high temperature evaporative emission testing have created a strong need to more capable purge strategies.
Traditionally, engine control systems have treated canister gases as a disturbance to the engine fueling and this often required compromise between the desire for improved evaporative emission control and the need for flawless driveability and fuel control in a variety of operating conditions and with a multiplicity of commercial fuels of varying quality. Steadily lower tailpipe emission requirements have made the more careful integration of vapor (purge) and liquid (fuel injector) delivery to the engine essential to robustly achieve the level of fuel control required for extremely low tailpipe emissions for both test cycle and real world conditions and fuels. Accordingly, engine control strategies have been proposed in which the calculation of the injector fuel quantity takes into account the quantity of purge fuel contained in the intake air ingested into the cylinder. See, for example, U.S. Pat. No. 5,596,972 to Sultan et al. In the Sultan et al. system, a physical hydrocarbon sensor is used to determine the concentration of fuel vapors in the purge gas and this estimate of the purge fuel vapor is used to determine the quantity of fuel to be delivered by the injector and to control the flow rate of purge gas into the intake manifold.